Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 182026

Area Forecast Discussion
National Weather Service Riverton WY
126 PM MST Sun Feb 18 2018

.SHORT TERM...(This evening through Wednesday)
Issued at 122 PM MST Sun Feb 18 2018

Snow, wind, blowing snow, drifting snow, falling temperatures, slick
roads and bitter cold wind chills are gradually engulfing the area
or will by tonight. Snowfall amounts were pretty solid in the nw
sections and generally a little lighter than expected in the
southwest. The far north on the other hand is exceeding expectations
with general a couple more inches than expected from Cody over to
GEY and BYG. Increased those amounts for the storm and upgraded BYG
to a warning due to widespread amounts over 6 inches and strong wind
continuing. Cold front is chugging swd as expected into the central
zones with snow developing quickly behind it. Complex jet structure
through tomorrow with current right entrance region supporting some
heavier snow in the north along with lead trough qg support. This
initial jet moves off to the east while a second one quickly
replaces it for more right entrance region support sagging south
tonight. At the same time, the main trough digging into the Great
Basin spits out its own jet streak which rounds the base and heads
towards our sern zones later tonight through Monday morning with
increasing qg forcing. We also see increasing mid level qg
forcing resulting in some significant omega in a fairly deep layer
across Natrona County. GFS is strongest with this signature
giving the CPR area over 20 (21) inches of snow by the time all is
said and done. The other models are more in the 8 to 12 range.
Still some uncertainty (low to moderate confidence) that the
dynamics will be that strong as far north as Natrona later tonight
and Monday (or perhaps not as long). Still possible but opted to
just bump Casper some more with 10 to 12 inches (more towards 12
on the south side). The NAM has actually backed away some from
this signature but is still giving CPR 10 inches. They both hit
Johnson pretty hard with widespread warning amounts with up to a
foot in srn Johnson. Further west in Fremont we should still see a
period of upper support tonight with an increase in snowfall
(once it becomes widespread here in the nest couple hours) rates.
Best signature remains east of us but still an expected period of
upper support to go with the upslope and also potential mid level
circulation. End result should still be a solid winter weather
advisory. 3 to 6 across the area. The CPR signature will also
affect ern Sweetwater overnight through Monday with periods of
moderate to heavy snow so warning down there still looks good. One
change in the ern zones was to extend the highlights about 6
hours. So 00z Tue in BYG, 03z Tue for Kaycee and 06z Tue for CPR.
Otherwise, it looks good. Temperatures will be on a downward
spiral through Tuesday morning. Only clouds in the ern half could
keep temps up somewhat Tuesday morning but still bitter cold. Any
clearing will drop temps even more. Bitter cold days Monday and
Tuesday could possibly lead to Wednesday morning being the coldest
day under a clear sky. Either way, it`ll be quite the shocker
with lows below zero and highs in the single digits through
Tuesday. Even struggling to get to zero in the north Monday.
Trough axis doesn`t actually ever swing east of us as it reloads
on Wednesday with another shortwave diving into mean trough. That
system will likely change our ocnl mtn flurries to light snow
later Wednesday.

.LONG TERM...(Wednesday night through Sunday)
Issued at 122 PM MST Sun Feb 18 2018

Given all the active weather in the first 36 to 48 hours we made
only minor tweaks to the long term. At this point, the reasoning is
the same with well below normal temperatures remaining over the area
into next weekend. However, with the longer days and stronger late
February sun, the air mass will likely modify a little each day and
raise temperatures somewhat. As for precipitation, one system dives
into the northwest Wednesday and could bring something to western
and southern portions of Wyoming but at this point the bulk of the
lift looks remain out of the area. A couple other systems may move
toward the area toward the weekend but with models continue to
struggle with intensity, location and timing so as explained
earlier, few changes were made.


.AVIATION...(For the 00Z TAFS through 00Z Monday afternoon)
Issued at 122 PM MST Sun Feb 18 2018

West of the Continental Divide...KJAC, KBPI, KPNA and KRKS

Mainly light snow with low VFR to MVFR conditions will be the rule
through the period for all TAF sites except for KRKS as the bulk of
the moisture and lift shift into southwestern Wyoming. Occasional
and short lived IFR conditions may still be possible through 04Z
tonight with any heavier snow shower.Occasional to frequent mountain
obscurations will be still be found however. At KRKS, ceilings will
lower to MVR with some IFR conditions possible in snow and blowing
snow, especially from after 06Z to 19Z Monday. Conditions may
improve toward the latter half of the TAF period.

East of the Continental Divide...KCPR, KCOD, KRIW, KLND, and KWRL

MVFR to IFR conditions are expected to continue at all TAF sites
through 00Z. Some improvement will be noted after 02Z at most
locations along and north of a KDUB to KBYG like, including KCOD and
KWRL with snow lightening, although ceilings may remain low at
times. Periods of snow will continue through the period at KRIW,
KLND and KCPR, with the lowest ceilings and visibilities at KCPR.
Wind should decrease tonight and be mainly light to moderate on

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.


Issued AT 122 PM MST Sun Feb 18 2018

A large and brutally cold winter weather system will engulf the
forecast area tonight through Tuesday. Almost all of the region will
receive precipitation of one kind or another by the end of the day
on Monday, including possible heavy snow at times. Then, extremely
cold conditions will overtake the region in the wake of an exiting
cold front for both Tuesday and Wednesday. Smoke dispersion will be
poor to fair (east of the Divide) to very good (west of the divide)
both today and Monday.


Winter Storm Warning until 11 PM MST Monday for WYZ029-030.

Winter Storm Warning until 11 PM MST Monday for WYZ019-020-022.

Winter Weather Advisory until 2 PM MST Monday for WYZ017-018.

Winter Storm Warning until 5 PM MST this afternoon for WYZ001-

Winter Storm Warning until 8 PM MST Monday for WYZ011.

Winter Storm Warning until 5 PM MST Monday for WYZ010.

Winter Weather Advisory until 2 PM MST Monday for WYZ005>009-016.

Winter Storm Warning until 2 PM MST Monday for WYZ015.

Winter Storm Warning until 8 AM MST Monday for WYZ027.

Winter Weather Advisory until 11 PM MST Monday for WYZ028.

Winter Weather Advisory until 11 AM MST Monday for WYZ003-004.



LONG TERM...Hattings
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